July 27 (Reuters) - Google Inc retook the offensive against thousands of authors claiming it copied their works without permission, and urged the dismissal of a class-action lawsuit arising from its ambitious plan to build the world's largest digital book library.

Friday's request by the world's largest search engine company followed a federal judge's March 2011 rejection of a sweeping $125 million settlement of the now seven-year-old case. Talks to revive an accord later broke down.

Google has scanned more than 15 million books since agreeing in 2004 with big research libraries, including the University of California and University of Michigan, to digitize current and out-of-print works for its Google Books website.

While the company planned to provide only snippets online to comply with copyright laws governing fair use, The Authors Guild and groups representing photographers and graphic artists complained that it amounted to "massive copyright infringement."

In a filing with the U.S. district court in Manhattan, Google said authors have shown no economic harm from its scanning and display of their works, and the creation of a searchable index to find them.

The company also said authors actually benefit because the database helps people find and buy their books, and that there is a "significant public benefit" from providing access to information that might otherwise not be found.

Lawyers for The Authors Guild did not immediately respond to requests for comment. Novelist-lawyer Scott Turow, president of that group, did not immediately respond to an emailed request for comment. Responses to Google's filing are due on Aug. 24.

In rejecting the $125 million accord, Judge Denny Chin had said it went too far because it gave Google a "de facto monopoly" to copy books en masse without permission and served to "further entrench" its market power in online searches.

The United States, Amazon.com Inc and Microsoft Corp had been among those to raise antitrust concerns about the settlement.

Chin began overseeing the Google case as a trial judge and kept jurisdiction after he was elevated in 2010 to the federal appeals court in New York.

He granted class-action status to authors in May, and said groups representing photographers and graphic artists may also sue.

The case is The Authors Guild et al v. Google Inc, U.S. District Court, Southern District of New York, No. 05-08136.